A local access cable network contains nodes which diverge into a network of branching coaxial cables that terminate in end units. Amplifiers placed along the branches compensate for attenuation losses along the branches and for coupling losses at the junctions. The branching network resembles an upside-down tree with the node at the root. Upstream communication along the branches to the node represents more problems than the downstream communication for two reasons.
First, the node receiver at the root of the tree receives the sum of noise from all the amplifiers in the entire network as well as the sum of ingress noise at all end units. On the other hand the receiver at an end unit gets only the noise of the amplifiers along the particular path between itself and the node and from the local ingress noise. Due to this increased noise, in a given physical bandwidth, the upstream traffic is of necessity considerably slower than the downstream traffic.
Second, downstream communication represents only a multiplexing problem, whereas upstream communication constitutes a multiple access problem to a shared medium. Multiple access problems arise in various situations and many solutions have been proposed and several are in use.
An object of this invention is to maximize the throughput for any mix of traffic with arbitrary time varying rates in the upstream direction.